Risk factors for postpartum readmission: a prediction model in Iranian pregnant women

Background Postpartum readmissions (PPRs) are an important indicator of maternal postpartum complications and the quality of medical services and are important for reducing medical costs. The present study aimed to investigate the risk factors affecting readmission after delivery in Imam Ali Hospital in Amol, Iran. Methods This retrospective cohort study was conducted on the mothers who were readmitted after delivery within 30 days, at Imam Ali Hospital (2019–2023). The demographic and obstetrics characteristics were identified through the registry system. Univariate and multivariate logistic regressions with odds ratios (ORs) and 95% CIs were carried out. To identify the most important variables by machine learning methods, a random forest model was used. The data were analyzed using SPSS 22 software and R (4.1.3) at a significant level of 0.05. Results Among 13,983 deliveries 164 (1.2%) had readmission after delivery. The most prevalent cause of readmission after delivery was infection (59.7%). The chance of readmission for women who underwent elective cesarean section and women who experienced labor pain onset by induction of labor was twice and 1.5 times greater than that among women who experienced spontaneous labor pain, respectively. Women with pregnancy complications had more than 2 times the chance of readmission. Cesarean section increased the chance of readmission by 2.69 times compared to normal vaginal delivery. Conclusion The method of labor pain onset, mode of delivery, and complications during pregnancy were the most important factors related to readmission after childbirth.


Background
Two-thirds of maternal deaths in developing countries occur after childbirth, and 80% of them occur in the first week after childbirth [1,2].According to the mortality rate of mothers in the puerperium, this period is considered to be important [3,4].The quality of maternal care during delivery and immediately after delivery is recognized as crucial for improving maternal care [5,6].Readmission after delivery is one of the mothers' morbidity indicators [7], as is maternal quality of care during delivery and postpartum [8].Readmission refers to the unplanned or emergency return of the patient within a certain time after discharge from the hospital [9].It is a criterion for determining the quality of health and medical care [10].In addition, hospital readmissions have important economic consequences and may account for up to 20% of total healthcare costs [11].
Readmission within a short period after discharge from the hospital can indicate a deficiency in the care provided during admission to the hospital or in the follow-up care Page 2 of 8 Firouzbakht et al.BMC Pregnancy and Childbirth (2024) 24:466 after discharge.For example, postsurgical infection may occur due to inadequate antibiotic prophylaxis, improper antiseptic techniques, the presence of a foreign body, or early discharge from the hospital.Moreover, there was a lack of adequate follow-up care due to social determinants (race, lack of social support, unemployment and lack of access to a proper transportation system).However, not all readmissions reflect deficiencies in care at the time of admission or deficiencies in the follow-up care system.The majority of these cases occur due to the onset of new illnesses unrelated to hospitalization or the progression of chronic disease, regardless of the type of care provided.It is estimated that only 9-48% of readmissions are associated with substandard care during hospitalization, such as a lack of complete treatment, unstable conditions at the time of discharge, or inadequate post discharge care [10,12].Although the hospital readmission rate is an indicator of quality [10], the postpartum readmission rate is not considered a quality indicator in maternity care [8].Most obstetric complications occur while the mother is still in the hospital.Considering that the physiology of pregnancy continues for several months, a large number of complications related to pregnancy or childbirth may occur after discharge, requiring readmission [13].
During the last two decades, the total rate of readmission after delivery has been reported to be 1-2% [7,[14][15][16][17].The rate was significantly greater among women who underwent cesarean section than among those who underwent NVD [9,18,19].The main reasons for readmission after childbirth are bleeding, infection and high blood pressure [15,19].The majority of postpartum hospitalizations are readmissions of women who have given birth in THE hospitals [20].Over the past decade, postpartum readmissions have increased by 27% (2% of all childbirths) [3], accounting for approximately 18% of all severe maternal complications [13,21].There are few related studies about readmission after childbirth in Iran [9,22].This study aimed to investigate the risk factors for readmission after childbirth in a hospital in northern Iran.

Design
This was a retrospective cohort study.The data of all pregnant women who gave birth from April 2019 to March 2023 at Imam Ali Hospital, Amol, Iran, were assessed.

Data collection
All the information was accessed through the registry system of the Ministry of Health (Iman).The information of all the women referred to maternity hospitals for delivery (gestational age > 26 weeks), throughout the country was recorded from the time of admission to the maternity hospital, during delivery and until 2 h after birth The following information was collected for the present study: maternal characteristics including age, education level, place of residence (urban-rural), insurance status, BMI, number of pregnancies, method of labor pain onset (spontaneous, induction and elective cesarean section), high-risk pregnancy status (yes, no), pregnancy complications (diabetes, gestational hypertension, preeclampsia, anemia, heart disease and other disease), risk factor for childbirth status (yes-no), type of delivery risk factor (rupture of the membranes for more than 18 h, abruption placenta, stained meconium), birth intervention status (yes-no), type of intervention (episiotomy), mode of delivery (NVD, cesarean section), adverse events after deliver (transfer of the mother to the operating room after delivery, transfer to the intensive care unit or death of the mother), and newborn weight.We included in the study all Iranian women that registered in the Iman from April 2019 to March 2023.
Mothers' readmissions after childbirth were identified by using the diagnostic codes of the International Classification of Diseases, 9th and 10th revisions, and clinical modifications (ICD-9-CM and 1cd-10-CM) [23].Postpartum hospitalization (i.e., readmission) was assessed using the fifth digit "4" in the ICD-9-CM codes for primary or secondary pregnancy-related complications.The ICD-9-CM v24 code is listed for each diagnosis, and related group codes were identified by postnatal diagnosis [13].

Data analysis
The patients' descriptive information was reported using the mean and standard deviation or by numerical value and percentage.Binary logistic regression analysis was used to investigate separately (crud effects) and simultaneously (adjusted effects) the relationships between variables predicting mothers' readmission in the postpartum period.Since some factors can affect this relationship, these variables were considered for adjustment in the final analysis.Variables that affected the relationships between predictive variables were considered for adjustment in the final analysis.The backward method was used in the multivariate analysis, and the remaining variables in the final model are presented.The odds ratio (OR) and 95% confidence interval (CI) were used to determine the effect size in the model.Furthermore, the random forest model was also used to identify the most important variables.In forest models, one of the most important indicators is the Gini coefficient index, which is used to identify the importance of variables for predicting the readmission of mothers in the postpartum period.The data were analyzed using SPSS 22 software and R (4.1.3).The significance level for the tests was considered < 0.05.

Results
A total of 13,983 deliveries were performed in the hospital between 2019 and 2023.In the present study, the mean and standard deviation of the ages of the pregnant women were 29.53 ± 6.02 years, ranging from 13 to 52 years.A total of 97.4% of the patients had Iranian citizenship, and 66.7% were city residents.More than half of the deliveries were by cesarean Sect.(56.3%).The onset of labor pain was induced in 48.3% of patients.Gestational diabetes and preeclampsia were observed in 5.5% and 1.4%, respectively.
Delivery risk factors and pregnancy complications were reported in 13.6% and 10.8%, respectively.Delivery intervention and delivery complications were observed in 36.4% and 0.4%, respectively.
Univariate and multivariate regression analyses of the variables influencing readmission after childbirth revealed that the labor pain onset method and pregnancy complications were related to readmission.Therefore, these two variables were identified as independent and strong predictors for readmission.(Table 2).
Moreover, the results showed that compared with NVD, cesarean delivery significantly increased the chance of readmission by 2.69 times (95% CI: 1.86 to 3.89, P = 0.003).Women who underwent obstetric interventions such as episiotomy had a 37% lower chance of readmission.
In the present study, mothers older than 35 years and with a BMI greater than 25 had a greater chance of readmission (95% CI: 0.76 to 1.64, P = 0.623, OR = 1.10 and 95% CI: 0.59 to 2.27, P = 0.67, OR = 1.15, respectively).However, this relationship was not significant.
The results of the random forest model based on the variables in the study showed that all the variables were important, and none of the variables were removed from the model.Figure 1 shows the importance estimated by the conditional forest algorithm.The importance of variables based on the Gini importance index (mean decrease Gini) showed that the most important variable was the method of labor pain onset (4.06%), and gravidity (4.04%) and newborn weight (3.15%) were identified in the next categories for predicting readmission in the postpartum period.(Fig. 1).

Discussion
This study aimed to determine the factors related to readmission after childbirth.The method of labor pain onset, mode of delivery, and pregnancy complications were identified as the most important factors related to readmission to the hospital.In the present study, women who underwent cesarean section and induced labor were more likely to be readmitted after delivery than women who underwent spontaneous delivery.Studies have reported that increasing the length of labor [24], prolonging the rupture of membranes, increasing the chance of postpartum hemorrhages [25], and increasing perineal rupture due to induction may increase the rate of readmission [26].In other studies, the mode of delivery [27][28][29][30], induction of labor [24], and pregnancy complications [16,[31][32][33] have been reported to be factors related to readmission.
In the present study, performing an episiotomy was associated with a decrease in the rate of readmission after childbirth.Performing an episiotomy can reduce severe perineal tears and therefore affect the rate of readmission.Another study reported that performing an episiotomy was associated with a reduction in perineal tearing [26].
The rate of readmission after childbirth reported in other studies ranged from 1.2 to 16.2% [17,[34][35][36].This rate in our study was 1.2%.However, referring women to other hospitals or other cities after giving birth can also affect the reported rate.
The results of the study revealed a greater chance of readmission in mothers with a history of diabetes and hypertension during pregnancy.Several studies have shown that these complications are risk factors for readmission after childbirth [31,33,32,37].Women with diabetes, especially diabetes type 1, as well as people with poor glycemic control during pregnancy, had a greater chance of being readmitted, especially due to infection.These results show the importance of multidisciplinary care for mothers and the control of complications during pregnancy [2].
Another related factor to readmission was the mother's age over 35 years.Researcher reported, women over 35 years were more likely to be re-hospitalized after childbirth due to severe maternal complications.Older age was associated with higher complications during pregnancy, readmission after delivery, and adverse neonatal outcomes [38].
The results of the study indicated that the chance of readmission among obese women was greater than that among women with a normal BMI.However, the difference was not statistically significant.The results of other studies [8,30] showed that women with a high BMI had a greater risk for diabetes and readmission due to infection.In the present study, the main causes of readmission were surgical incision problems (i.e., infection, wound dehiscence and hematoma) and postpartum bleeding.These findings are in line with numerous studies concluding that bleeding, infection, and hypertension are the main reasons for readmission after childbirth [15,16,19].
A mother's readmission within a short interval after delivery is stressful for the mother, newborn, and family.Identifying the factors related to re-hospitalization can be considered in care protocols for mothers after childbirth to minimize severe complications after childbirth and reduce maternal mortality.The World Health Organization has recommended postpartum care at 24 h, 3 days (24 to 72 h after delivery), 7 to 14 days, and six weeks after delivery [19,39].Although all readmissions are not preventable, identifying women at risk for more preventive care is essential.Recent clinical recommendations emphasize improving postpartum care (as the fourth trimester of pregnancy).
According to the recommendation of the ACOG, "to optimize the maternal and child health, postpartum care should be considered as an ongoing process and health services and supports must be based on individual needs" [40].A standard visit may be appropriate for low-risk women, but high-risk women require special care [41].
According to the definition of quality of patient discharge from the hospital (as the experience of patients with sufficient education and resources at the time of discharge) and its association with a lower readmission rate among the general population [42,43], providing suitable protocols for patient discharge and comprehensive assessments of the individual and educational interventions are recommended [15].

Strengths and limitations
There were study limitations in the interpretation of the results.First, although information related to childbirth was collected through a comprehensive information system, information records were missing, which can affect the results.Second, due to the closeness of the city (Amol) to the capital city (Tehran) and other cities that have more advanced academic centers, it is possible that several cases of readmission were readmitted to other hospitals in nearby cities.
One of the strengths of this study was the large sample size.On the other hand, all the data of the study were related to one hospital, which can reduce the dispersion in the method of data recording.To the best of our knowledge, the present study is the first study with a large sample that aimed to determine the factors related to readmission in Iran.

Conclusion
Our results highlighted that the most important factors related to readmission after childbirth were the method of labor pain onset, mode of delivery and complications during pregnancy.All the risk factors we identified were mostly related to demographic and obstetric characteristics.Improving the quality of care during pregnancy as well as postpartum care for high-risk pregnant women seems to be the golden key to reducing readmission.Additionally, interventions such as women's education regarding early warning signs after childbirth to prevent potentially life-threatening complications are necessary.

Clinical application
Since a considerable portion of maternal morbidity and mortality are related to the postpartum period, understanding the importance of the quality of inpatient and outpatient postpartum care in improving maternal outcomes is essential.Identifying at-risk women and designing purposeful interventions might reduce mortality and morbidity.

Fig. 1
Fig. 1 Random forest model to predict the most important factors in the readmission of mothers in the postpartum period

Table 1
Demographics and obstetrics characteristics of admitted women in the maternity hospital (Imam Ali), 2019-2023

Table 2
Univariate logistic regression analysis in readmission after childbirth

Table 3
Multivariate logistic regression analysis (adjusted effects) in readmission after childbirth (backward model)Variables included in the Backward model: Age, Education, Insurance, Residence, BMI, Gravidity, onset of Labor Pain, Complication pregnancy, Delivery risk, Delivery intervention, Delivery type, and Baby weigh